If You Sit a Lot, Read this

Lots of sitting and little physical activity can be lethal

Move more, sit less

Overwhelming evidence shows that Keep Moving reduces our risk of chronic diseases and premature death. Evidence also shows that many hours of sitting has the opposite effects. Would people who sit a lot and who engage in high levels of physical activity escape the downside health risks of lots of sitting? A recent study in the prestigious journal, Lancet, answered this question. An international team of researchers conducted an analysis of 16 published reports that evaluated mortality risk in conjunction with amounts of physical activity and sitting time. The studies included over a million subjects with follow-up periods ranging from 2-18 years.

As expected, risk of premature death increased as the number of daily hours of sitting increased. For the three lowest levels of weekly moderate-intensity physical activity (less than 5 minutes per day, less than 25 minutes per day, less than 50 minutes per day), the risk of premature death increased as the number of sitting hours increased. But at the highest level of moderate-intensity physical activity (more than 60 minutes per day), the risk of premature death did not increase as daily sitting time increased to more than 8 hours. This is huge! It means that you may eliminate the adverse effects of lots of sitting if you get more than one hour of moderate-intensity daily exercise each day.

The analysis was repeated using number of hours of TV watching as a measure of sitting time. The results were similar except that the highest level of physical activity reduced but did not eliminate the risk of premature death. Watching TV appears to be more toxic than simply sitting. This difference might arise from adverse effects on blood sugar and blood fats when plopping down in front of the TV soon after eating dinner. Especially a big dinner with lots of starchy and sugary foods. And especially if TV watching induces you to start snacking.

A recent review and meta-analysis of 34 studies extended the adverse effects of sedentary behavior to premature death arising from all-causes or cardiovascular disease, as well as incident type 2 diabetes. Even after accounting for varying levels of physical activity, all-cause and cardiovascular mortality increased non-linearly as the amount of total sedentary behavior increased. That is, the curve of risk bent upward as total sedentary behavior increased. The risk of all-cause and cardiovascular mortality increased even more as the amount of TV viewing increased. The risk of developing type 2 diabetes increased linearly as either total sedentary behavior or amount of TV viewing increased. For all-cause and cardiovascular mortality, risk increased above a threshold of 6-8 hours per day of total sitting and 3-4 hours per day of TV viewing, respectively. Do yourself a favor and trade one hour of TV viewing or other sitting time for one hour of moderate-intensity exercise each day.

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